Originally Posted by Flyin'Mom
What kind of weird little thrill does your friend get from leaving his phone on for every flight?
Believe me, I'm not a rule follower by nature...but this kind of defiant behavior, with no measurable benefit, is just as silly as the rule he is going against...IMHO, of course.

I leave my phone on in flight all the time. I recieve text messages as the signal fades in and out at certain times during the flight.
Sometimes I leave my laptop on -- not hibernated! Why would I do this? Maybe I'm compiling a program and don't want it interrupted. Or maybe I just don't feel like powering my laptop off.
Whatever the case, if it were dangerous, as others have mentioned, planes would be falling out of the sky. It's not dangerous -- the feds just have no idea what they're doing in this regard.
Oh, and one other thing. If there's some sort of massive problem on the plane, I'm doing absolutely everything I have to to make it out alive. EVEN if I have my headphones on.